<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      (function () {
        /*
 indexOf()  查找到返回下标  ，查找不到返回-1
 lastIndexOf 往后查找
      */
        let str = 'a b c';
        console.log(str.indexOf('a')); // 0
        console.log(str.indexOf('d')); //-1
      })();
    </script>
  </body>
</html>
